1. FIELD OF THE INVENTION
The present invention relates to hydraulic brake assistance devices and more particularly to such a device for a dual brake circuit of mixed hydrodynamic (known as "full power") and hydrostatic operation.
2. DESCRIPTION OF THE PRIOR ART
A so-called "full power" hydraulic assistance device is known from French Patent Application No. 8,502,824, filed on Feb. 27, 1985, which device comprises two piston means delimiting two master cylinder chambers and each having a return valve means to the tank. The device also comprises two high pressure valve means, a first incorporated in the first piston means and a second in an element closing the bore of the device. The device may function in the hydrodynamic mode and, in the event of failure of a high pressure circuit, in the hydrostatic mode as a conventional master cylinder.
Despite its advantages, this device has minor drawbacks in that the pedal travel perceived by the driver of the vehicle is too short. Modern vehicle manufacturers request that the pedal travel should be more progressive in order to improve driving comfort.